Agriculture Reference
In-Depth Information
Table 4.9.2.
Nutrient offtakes from cash crops (N, P and K kg
−
1
ha
−
1
year
−
1
). The values in
paretheses are the standard error.
Crop yield
(t ha
−
1
)
Course of rotation offtake per
course
Mean
offtake
per
course
Mean
offtake
per
rotation
Rotation
2
3
4
2
3
4
Nitrogen
A
4.29
a
(1.3) 2.64
a
(1.3) 2.03
a
(1.3)
61 (2.65)
36 (3.57) 25 (0.18)
41
122
B
29.35
b
(8.8) 4.29
a
(1.3) 3.19
a
(1.3)
87 (0.02)
64 (3.14) 39 (0.14)
63
190
14.41
c
(3.6)
C
3.75
a
(1.3) 4.10
a
(1.1) 3.99
a
(1.3)
56 (3.07) 150 (8.59) 57 (3.12)
88
263
Phosphorus
A
25 (1.93)
15 (1.53) 12 (3.60)
17
52
B
61 (4.87)
26 (2.02) 19 (2.06)
35
106
C
23 (1.96)
29 (1.83) 24 (1.76)
25
76
Potassium
A
21 (1.04)
14 (1.30) 15 (1.32)
17
50
B
153 (4.18)
20 (1.32) 16 (1.48)
63
189
C
19 (1.06)
49 (3.24) 20 (1.37)
29
88
a
Yields adjusted to standard 15% moisture content.
b
Total yield.
c
Ware (marketable) yield.
conventional agricultural systems that a change from grass to arable
production will result in losses of soil organic matter. To date, little work
has been carried out on the effects of changing from an organic ley-arable
system to an organic stockless system. However, it seems likely that the
changes in soil organic matter levels between the first 4 years (cycle 1) and
the following years (cycles 2 and 3) are a result of the transition from a grass
to an arable-based system.
All three rotations presented here were experimental and were never
meant to represent organic practice. It is clear from this study that organic
rotations with only 25% or less fertility building and only recycling crop
residues result in a decline in soil organic matter levels. Changes in the
setaside regulations, after this trial was established, have allowed organic
farmers to use setaside as a means for fertility building for up to 2 years.
The crop needs for available P appear to be adequately met through
the application of rock phosphate to the green manure crops. Cropping
sequence appears to have an effect on the availability of P from the
slow-release fertilizers (EFRC, 1993).
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